LibIMAP: Support for the FETCH command (*mostly)

This commit doesn't include support for FETCH BODY, because it's a bit
big already. Rest assured, FETCH is the most complicated IMAP command,
and we'll go back to simple boring ones shortly.

Userland/Libraries/LibIMAP/Objects.cpp

@@ -8,4 +8,105 @@
 
 namespace IMAP {
 
+String Sequence::serialize() const
+{
+    if (start == end) {
+        return AK::String::formatted("{}", start);
+    } else {
+        auto start_char = start != -1 ? String::formatted("{}", start) : "*";
+        auto end_char = end != -1 ? String::formatted("{}", end) : "*";
+        return String::formatted("{}:{}", start_char, end_char);
+    }
+}
+
+String FetchCommand::DataItem::Section::serialize() const
+{
+    StringBuilder headers_builder;
+    switch (type) {
+    case SectionType::Header:
+        return "HEADER";
+    case SectionType::HeaderFields:
+    case SectionType::HeaderFieldsNot: {
+        if (type == SectionType::HeaderFields)
+            headers_builder.append("HEADER.FIELDS (");
+        else
+            headers_builder.append("HEADERS.FIELDS.NOT (");
+
+        bool first = true;
+        for (auto& field : headers.value()) {
+            if (!first)
+                headers_builder.append(" ");
+            headers_builder.append(field);
+            first = false;
+        }
+        headers_builder.append(")");
+        return headers_builder.build();
+    }
+    case SectionType::Text:
+        return "TEXT";
+    case SectionType::Parts: {
+        StringBuilder sb;
+        bool first = true;
+        for (int part : parts.value()) {
+            if (!first)
+                sb.append(".");
+            sb.appendff("{}", part);
+            first = false;
+        }
+        if (ends_with_mime) {
+            sb.append(".MIME");
+        }
+        return sb.build();
+    }
+    }
+    VERIFY_NOT_REACHED();
+}
+String FetchCommand::DataItem::serialize() const
+{
+    switch (type) {
+    case DataItemType::Envelope:
+        return "ENVELOPE";
+    case DataItemType::Flags:
+        return "FLAGS";
+    case DataItemType::InternalDate:
+        return "INTERNALDATE";
+    case DataItemType::UID:
+        return "UID";
+    case DataItemType::PeekBody:
+        TODO();
+    case DataItemType::BodySection:
+        StringBuilder sb;
+        sb.appendff("BODY[{}]", section.value().serialize());
+        if (partial_fetch) {
+            sb.appendff("<{}.{}>", start, octets);
+        }
+
+        return sb.build();
+    }
+    VERIFY_NOT_REACHED();
+}
+String FetchCommand::serialize()
+{
+    StringBuilder sequence_builder;
+    bool first = true;
+    for (auto& sequence : sequence_set) {
+        if (!first) {
+            sequence_builder.append(",");
+        }
+        sequence_builder.append(sequence.serialize());
+        first = false;
+    }
+
+    StringBuilder data_items_builder;
+    first = true;
+    for (auto& data_item : data_items) {
+        if (!first) {
+            data_items_builder.append(" ");
+        }
+        data_items_builder.append(data_item.serialize());
+        first = false;
+    }
+
+    return AK::String::formatted("{} ({})", sequence_builder.build(), data_items_builder.build());
+}
 }